The present invention relates to an arrangement, method and device for measuring a current in a conductor.
An object of the present invention is to provide a method that is particularly simple to execute for producing a signal that characterizes a fault current in an electrical conductor that has at least three conductor ends. In this context, a fault current is understood to be a current that flows out of the conductor, or that flows into the conductor, at a fault point of the conductor, for example a short-circuit point, and thus not at one of the conductor ends.
In order to achieve this object, according to the present invention, a method is provided for producing a fault signal that characterizes a fault current of an electrical conductor that has at least three conductor ends, using current measurement devices that are arranged in such a way that one of the current measurement devices is attached at each conductor end of the conductor and the current measurement devices are connected via data lines. The method the current in the respective conductor ends is measured using the current measurement devices, and current measurement values are formed. A measurement value, formed from the current measurement values of the other current measurement devices using addition that respects the sign, is transmitted to a selected current measurement device, using the selected current measurement device, an overall current value is formed from the current measurement values thereof and the measurement value, using addition that respects the sign, and the fault signal, is produced using the selected current measurement device if the absolute value of the overall current value exceeds a predetermined threshold value. The sign-respecting addition of the current measurement values can take place in the time domain or in the frequency domain. If the method according to the present invention is used in a three-phase alternating current system, the method is executed separately for each phase, i.e. for each phase conductor; in this context, each phase can be switched off individually in the case of a fault current.
An advantage of the method according to the present invention is that it is very fast, because in the method, the current measurement values of the other current measurement devices are first combined, by sign-respecting addition, to form one measurement value, and subsequently only this measurement value is transmitted to the selected current measurement device. Since only this single measurement value need be transmitted to the selected current measurement device, the overall quantity of data to be transmitted is very small; this results in the particularly high speed of the method according to the present invention, since the smaller the amount of data to be transmitted, the less is time required for this. In addition, only a single computational step need be executed in the selected current measurement device, consisting in the addition of the transmitted measurement value to the measured current measurement value of the selected current measurement device; the transmission of the previously determined measurement value therefore relieves the selected current measurement device of further computational steps, likewise resulting in an increase in speed.
The object is also achieved by a method according to the present invention for producing a fault signal that characterizes a fault current of an electrical conductor having at least three conductor ends, using current measurement devices arranged in such a way that one of the current measurement devices is attached to each conductor end of the conductor and the current measurement devices are connected via data lines. In the method the current in the respective conductor ends is measured using the current measurement devices, with formation of current measurement values, and a measurement value, formed from the current measurement values of a first group of the remaining current measurement devices by sign-respecting addition, is transmitted to a selected current measurement device, and an additional measurement value, formed from the current measurement values of a second group of the remaining current measurement devices by sign-respecting addition, is transmitted to the selected current measurement device. The second group contains all current measurement devices except for the selected ones and the current measurement devices of the first group. Using the selected current measurement device, an overall current value is formed from the current measurement values thereof and the two measurement values through sign-respecting addition, and the fault signal is produced using the selected current measurement device if the absolute value of the overall current value exceeds a predetermined threshold value. The advantages cited in connection with the first method also hold for the second method according to the present invention. A particular advantage of the second method, is that in this method the current measurement devices can be divided into two groups and a separate measurement value can be formed for each of the two groups. This can, for example, be advantageous if the two groups of current measurement devices are separated from one another by a large spatial distance and the formation and transmission of a single measurement value to the selected current measurement device would cause a particularly high expense.
Moreover, an arrangement according to the present invention is provided with which a fault signal characterizing a fault current in an electrical conductor having at least three conductor ends can be formed in a particularly simple fashion.
This object is achieved by an arrangement for producing a fault signal that characterizes a fault current of an electrical conductor having at least three conductor ends. A current measurement device, attached to each conductor end of the conductor, measures the current in its respective conductor end with formation of a current measurement value. The current measurement devices in the arrangement are connected to one another electrically by means of data lines in a chain-type structure in such a way that each internal current measurement device in the chain is connected, with a measurement value input, to a measurement value output of the current measurement device arranged upstream therefrom, and is connected, with a measurement value output, to a measurement value input of the current measurement device arranged downstream therefrom. A first current measurement device of the two current measurement devices arranged externally in the chain is connected, with its measurement value output, to a measurement value input of the internal current measurement device arranged downstream therefrom. The second of the two external current measurement devices is connected, with a measurement value input, to the measurement value output of the internal current measurement device arranged upstream therefrom. Each internal current measurement device has an arithmetic unit that adds, in sign-respecting fashion, its current measurement value to a measurement value, present at its measurement value input, of the respective upstream current measurement device, so as to form a summation current measurement value, and outputs the summation current measurement value as a measurement value at its measurement value output. The second external current measurement device has a control unit that outputs the fault signal as soon as an overall current value, formed by sign-respecting addition from the measurement value of the upstream internal current measurement device and its current measurement value, exceeds a predetermined threshold value. An advantage of this arrangement is the particularly high speed with which the fault signal is produced, since not all the current measurement values of the other current measurement devices are transmitted individually to the second external current measurement device. Instead, only a single measurement value is transmitted that contains the current sums of the remaining current measurement devices. This results in a particularly rapid production of the fault signal, because the overall quantity of data to be transmitted to the second external current measurement device is relatively small, since only a single measurement value is to be transmitted. An additional advantage of the arrangement according to the present invention is that only relatively few data lines are necessary for connecting the current measurement devices; given a line having N conductor ends, in the chain-type arrangement of the current measurement devices only (Nxe2x88x921) data lines are required, whereas, in contrast, given an arrangement in which all current measurement devices are connected to one another N*(Nxe2x88x921) data lines are required.
In order that, in addition to the second external current measurement device, at least one internal current measurement device can also produce the fault signal, within the scope of a development of the arrangement, the internal current measurement devices may be connected to one another in such a way that an additional measurement value input of an internal current measurement device is connected to an additional measurement value output of the internal current measurement device arranged downstream therefrom, and an additional measurement value output of an internal current measurement device is connected to an additional measurement value input of the internal current measurement device arranged upstream therefrom. The first external current measurement device is connected, with a measurement value input, to an additional measurement value output of the internal current measurement device arranged downstream therefrom. The second external current measurement device is connected, with a measurement value output, to an additional measurement value input of the internal current measurement device arranged upstream therefrom. Each internal current measurement device has an additional arithmetic unit that adds, in sign-respecting fashion, the current measurement value of its own current measurement device to an additional measurement value, present at its additional measurement value input, of the downstream current measurement device, so as to form an additional summation current measurement value, and outputs the resulting additional summation current measurement value at its additional measurement value output as an additional measurement value. At least one of the internal current measurement devices has a control unit that produces the fault signal as soon as the overall current value, formed by sign-respecting addition from the measurement values present at its two measurement value inputs and its measured current measurement value, exceeds the predetermined threshold value. The advantage of this arrangement is that a plurality of current measurement devices of the arrangement are able to produce the fault signal, since all the current measurement devices are provided with the required items of current information; in such an arrangement, 2*(Nxe2x88x921) data lines are then required.
In order that the fault signal can also be produced using the first external current measurement device, the first external current measurement device may have a control unit that produces the fault signal as soon as the overall current valuexe2x80x94formed by sign-respecting addition from the measurement value present at its measurement value input and its measured current measurement valuexe2x80x94exceeds the predetermined threshold value.
A particularly high degree of reliability can be achieved in the arrangement according to the present invention if the two external current measurement devices are connected with one another by at least one additional data line via which the overall current value is transmitted. This is because in such an arrangement the respectively determined overall current value can be transmitted between the two external current measurement devices for monitoring purposes; for example, the two external current measurement devices can check the readiness for operation of the overall arrangement by comparing their respective overall current values. An additional advantage of the additional data line is that the arrangement according to the present invention can continue to be operated even if one of the data lines is interrupted by a disturbance.
Within the scope of the present invention, a current measurement device is also proposed that can be used in the method or in the arrangement according to the present invention. This is a current measurement device for measuring a current in a conductor having at least one measurement value input and at least one measurement value output, as well as an arithmetic unit that adds a current measurement value corresponding to the current to a current measurement value present at the at least one measurement value input, and outputs the resulting summation current measurement value at the at least one measurement value output. The advantage of the current measurement device according to the present invention is that it has an arithmetic unit with which, for example, summation current measurement values can be formed, as was explained above in connection with the method or the arrangement according to the present invention. The advantages described above in connection with the method and with the arrangement thus hold in corresponding fashion for the current measurement device according to the present invention.
In order to facilitate the installation of the current measurement device according to the present invention, it is proposed, within the scope of a development of the current measurement device, that the arithmetic unit have a device with which the sign of the current measurement value can be changed. Such a current measurement device has the advantage that when connecting the current measurement device to a conductor or to a conductor end no attention need be paid to the direction of the current in the conductor or conductor end, because the sign of the current measurement value determined by the current measurement device can be changed if necessary, so to speak retroactively. This may be for example, important with respect to the sign-respecting addition of the current measurement values in the inventive method for producing a fault signal, since in the formation of a summation current measurement value the signs are of course to be taken into account.
If in addition a fault signal is also to be formed using the inventive current measurement device, may be as advantageous if the current measurement device has a control unit that outputs a signal for a fault current as soon as the summation current measurement value exceeds a predetermined threshold value.